Apparatus for conveying bulk material

ABSTRACT

A pneumatic conveying system for bulk materials comprises a conveyor pipe and a bypass pipe which communicates with the conveyor pipe at several points through inlet and outlet openings, the free cross-section of the by-pass pipe being equal to between 10 and 20 percent of the free conveying cross-section of the conveyor pipe. The inlet and outlet openings are formed by radial cut-outs in the wall of the bypass pipe, the ducts of the pipe wall immediately following these cut-outs being in the form of tongues which block from 10 to 90 percent of the free crosssection of the bypass pipe.

United States Patent 1191 Muschelknautz et al. Sept. 18, 1973 APPARATUSFOR CONVEYING BULK 3.626.986 12/1971 Amberg 302/64 x MATERIAL FOREIGNPATENTS R APPLICATIONS lnventersr Edger Musehelkheutzi 1,151,173 /1966Great Britain 302/64 Leverkusen-Bayerwerk; Wolfgang Krambmck Leverkusen'both of Primary Examiner-Richard E. Aegerter Germany AssistantExaminer-4i. S. Lane [73] Assignee: Bayer Aktiengesellschaft, ypDinklage at Leverkusen, Germany 22 Filed: Dec. 23, 1971 [57] ABSTRACT[21] APPL No: 211,507 A pneumatic conveying system for bulk materialscomprises a conveyor plpe and a bypass pipe which communicates with theconveyor pipe at several points [30] Foreign Application Priority Datathrough inlet and outlet openings, the free cross- .Ian. 19, 1971Germany P 21 02 301.3 Section of the y- P being equal to between andpercent of the free conveying cross-section of 52 U.S. c1. 302/29,302/64 the conveyor p p The inlet and Outlet Openings are 51 Int. (11.;Bg 53/04 formed y redial cut-ems in the of the bypass p p 581 Field6rsem1i....; 302/64, 29, 31 the duets of the p p immediately followingthese 7 cut-outs being in the form of tongues which block from [56]References Ci d 7 10 to 90 percent of the free cross-section of thebypass UNITED STATES PATENTS 3,240,531 4/1966 Lipport et al 302/64 X 7Claims, 2 Drawing Figures 10a 72a 73121 f. b 72b 73b 70c 12 73c 23 70d72d 73d //6j 3 i 176/ 3 21/ 3 77d '76 l W I v1' 1 APPARATUS FORCONVEYING BULK MATERIAL This invention relates to an apparatus forpneumatic or hydraulic conveying of bulk material in dust, powder orgranular form.

In one known process (German Patent Specification 1,174,256), materialin dust, powder or granular form can be conveyed free from any danger ofblocking using a quantity and a flow-rate for the carrier medium of onlya fraction of the hitherto usual values. In this process the main streamforming the mixture of product and carrier medium in the pipeline ispartly branched off at a number of junctions following one another atshort intervals longitudinally of the flow direction and the componentstream flows through the particular branch separately from the mainstream and is guided back into the main stream just upstream of the nextjunction.

This process was carried out in an apparatus comprising a conveyor pipewith branch pipes running parallel thereto which, at both ends, openinto the conveyor pipe, a number of short branch pipes being arrangedone behind the other longitudinally of the main pipeline with the outletopening of each branch pipe opening just upstream of the inlet openingof the next branch pipe. In this case, the branch pipes are preferablyarranged inside the conveyor pipe, or alternatively they are formed froma pipe arranged inside the conveyor pipe which is bent at intervals andwhich is cut at the bends to form branch openings.

In order to convey bulk materials safely by pneumatic or hydraulicmeans, the resistance which is built-up as the carrier medium flowsthrough the branch pipe must be considerably greater than the flowresistance which is directed against the main stream in the conveyorpipe, otherwise most or all of the flow medium would flow through thebranch pipe without taking part in the conveying operation. The minimumpressure difference between the static pressures in front of and behinda plug of material of the kind frequently formed in pneumatic conveyingwhich is necessary for the further movement thereof, increasesprogressively with increasing plug length due to the wedging effect ofthe particles of material both against one another and against the wall.In the case of an excessively long plug of material, the conveyingpressure available is no longer sufficient to apply the pressuredifference required to shift the plug. In this case, the carrier mediumflows in surges into and through the branch pipe through the inletopening situated upstream of the plug.

The static pressure of the unblocked conveyor pipe lying upstream of theplug, reduced by the particular flow resistance of the branch pipesection, is applied to the plug of material through the outlet-and inletopenings in the branch pipe which it has closed. Although the staticpressure upstream of the plug of material is unable to shift the entireplug of material, the pressure is sufficient for separating the lastplug fragment (looking in the direction of flow) which at most extendsover a length corresponding to the interval between two outlet openingsin the branch pipe, providing the flow resistance. of the branch pipecarrying the last plug fragment is greater than the resistance requiredto shift the plug fragment. Once the last fragment of the plug ofmaterial has been broken up and carried away, the separation process isrepeated with eachpreceding fragment of the plug until the process iscompleted.

German Patent Specification l,l74,256 discloses various embodiments ofthe branch pipes some of which are arranged outside and some inside theconveyor pipe. In this case, the necessary flow resistance of the branchpipe between two branch openings which arises out of the pressurerequired to shift a plug of material situated between these twoopenings, is generated by a vary narrow cross-section of the branchpipe.

Safe pneumatic or hydraulic conveying at low rates of flow of thecarrier medium is only ensured if the relatively narrow branch pipesremain free from deposits of material. However, this is only the casewith nonsticking, free-flowing fine-grained bulk materials. In the caseof bulk materials which form a light wall deposit or whose grain sizerange covers particles a few mm in diameter, the narrow branch pipessoon become blocked and hence ineffective.

Swiss Patent Specification 459,060 discloses branch pipes of relativelylarge cross-section which are formed by welding a U-shaped bypass ducton to the conveyor pipe, or by inserting and screwing a plate into theconveyor pipe by which a circular segment of the pipe is separated 05.Inside the U-shaped bypass duct, branch openings are drilled through thewall of the conveyor pipe. In the segment-like bypass duct, the branchopenings are in the form of holes drilled into the inserted strip ofmetal. The requisite minimum pressure loss in the bypass duct isobtained by incorporating chicanes between two branch openings.

These particular embodiments of the bypass duct provide for extremelysafe conveying at low conveying pressures and with a low throughput ofcarrier medium. A light wall deposit and even relatively large particlesof material which enter the bypass duct do not give rise to anydisturbances.

Unfortunately, the costs involves in making the conveyor pipes with thebypass duct welded on to them or formed by inserting the strip of metal,are so high that, especially in conveyor systems with low or averagethroughputs of material, the increased costs cannot be covered by thesaving of energy by comparison with a conventionally built conveyorsystem. One particular disadvantage of the segment-like bypass duct isthat a considerable proportion of the conveyor pipe crosssection isoccupied by the bypass duct. In addition, it is extremely difiicult tofix the edges of the inserted strip tightly to the wall of the pipe.

An object of the invention is to provide an operationally safeembodiment of a conveyor pipe with a bypass duct which is easy andinexpensive to produce.

According to the invention, there is provided an ap paratus forpneumatic or hydraulic conveying of bulk materials comprising a conveyorpipeline with branch pipes parallel thereto which at both ends openinto' the conveyor pipe, a number of short branch pipes being arrangedone behind the other longitudinally of the pipeline whilst the outletopening of each branch pipe opens upstream of an inlet opening theadjacent branch pipe on the downstream side thereof, wherein the branchpipes consist of a bypass pipe which is fixed inside the conveyor pipeto the wall thereof and whose free cross-section is from 10 to 20percent of the free cross-section of the conveyor pipe and in which theinlet openings and outlet openings are formed by radial cut-outs in thewall of the bypass pipe, the ends of the pipe wall immediatelydownstream of the openings projecting as tongues into the bypass pipeagainst the main conveying direction and blocking from to 90 percent ofthe free cross-section of the bypass pipe.

Thus, for example, in the bypass pipe, the inlet openings are preferablyeach provided (looking in the conveying direction) behind an outletopening at a distance corresponding to between one and two times theinternal diameter of the bypass pipe.

The tongues of the outlet openings advantageously block from 30 to 90percent of the free cross-section of the bypass pipe.

It has proved to be similarly advantageous for the tongues of the inletopenings to block from 10 to 70 percent of the free cross-section of thebypass pipe.

All these special measures contribute towards the build up in the bypasspipe of pressure conditions particularly favourable for conveying andfor substantially avoiding deposits of material in the bypass pipe. Theconditions most suitable for a given material can be determined bytests.

By virtue of the bypass pipe designed in accordance with the invention,the carrier medium is able, in the event of a relatively long plug ofmaterial being formed in the conveyor pipe, to penetrate into the bypasspipe through the branch openings upstream of the plug. By virtue of therelatively large cross-section of the bypass pipe, there is no danger ofthe bypass pipe becoming blocked. Material conveyed through the bypasspipe is predominantly carried forward in the form of strands along thebottom thereof. Under the effect of the tongue of the following outletopening which is pressed into the bypass pipe, these strands of materialare peeled off and guided back into the conveyor pipe. By contrast, thecarrier medium conveys material in the form of a drifting cloud and isable to flow almost unhindered along the bypass pipe through theunblocked cross-section thereof. One particular advantage of this isthat the material conveyed through the bypass pipe does not have to passany constrictions so that there is no danger of blockage.

Conventional types of bypass pipe have a constant pressure losscoefficient, as measured between two outlet openings, which isunaffected by the flow rate or delivery rate. By contrast, the pressureloss coefficient of the individual bypass pipe sections in the apparatusaccording to the invention is automatically adapted to the particulardelivery phase. Where the material is uniformly conveyed, the rate offlow in the bypass pipe is much lower than in the conveyor pipe due tothe relatively high pressure loss coefficient. It is'only when a plug ofmaterial is formed that the carrier medium flows in surges into thebypass pipe through the inlet and outlet openings upstream of the plugof material. The static pressure prevailing upstream of the plug ofmaterial, acts on the plug of material through the following outletopening in the bypass pipe which is closed by the plug of material.

If the plug is short, that fragment following the outlet opening in thedirection of flow is carried off. By contrast, if the plug extends overseveral sections of the bypass pipe, the carrier medium is able tocontinue flowing through the bypass pipe above the tongues of the outletand inlet openings projecting into the bypass pipe. The tongue of theoutlet opening directed against the flow direction in the bypass pipeproduces considerable constriction of the flow in the following sectionof the bypass pipe. As in an injector, a sharp propellant jet is formed.The effect of the reduced pressure which it produces in the areasurrounding it is that a little material is sucked out of the plug ofmaterial into the bypass pipe through the inlet openings downstream ofthe outlet openings. By virtue of the fact that the material sucked inhas to be accelerated in the conveying direction, the pressure losscoefficient of the following bypass pipe section is increased. The plugof material is as it were hollowed out through the removal of materialfrom it under suction. As a result, part of the carrier medium is ableto flow out of the bypass pipe through the outlet opening and back inthrough the inlet opening. In this way, even more material is, so tospeak, worn away and the bullow or depression in the plug of materialbecomes larger, making it easier for the next plug fragment downstreamthereof to be broken away. If the static pressure is not sufficient forthis purpose, the delivery of material from the plug into the bypasspipe soon comes to a stop because the cross-section of the area hollowedout in the plug of material is too large and hence the rate of flowtherein too low to entrain further particles of material. The pressureloss coefficient of the outlet opening falls again and the carriermedium is able to flow almost unhindered to the next outlet openingwhere the sequence of events described above is repeated.

Once the final plug fragment (looking in the direction of flow) has beenbroken away, the pressure loss in the bypass pipe is reduced by anamount corresponding to the flow resistance of that section of thebypass pipe previously surrounded by the plug. As a result, an increasedquantity of carrier medium now flows through the bypass pipe with theeffect that material from the channels which have already been hollowedout below the inlet openings is sucked through the inlet opening intothat section of the bypass pipe upstream of the end of the plug.

In this way, the pressure loss in the bypass pipe sections is increasedagain, thus preventing the carrier medium from flowing unhindered aroundthe rest of the plug through the bypass pipe.

The bypass pipe used in the invention is distinguished from conventionalembodiments by its high reliability in operation, and by the fact thatthe costs involved in making the conveyor pipe integrally with thebypass pipe can be reduced in this way to as little as one quarter sothat the use of the conventional process for separating columns ofmaterial in the pneumatic or hydraulic conveying of bulk materials isnow economically justified in almost every case.

The invention is described in detail in the following with reference toan embodiment illustrated purely diagrammatically in the accompanyingdrawings, wherein:

FIG. 1 is a longitudinal section through the apparatus according to theinvention, and

FIG. 2a cross-section on the line A-A of FIG. 1.

In FIGS. 1 and 2, the apparatus consists of a conveyor pipeline 1 whichis divided into a conveyor pipe 2 and a bypass pipe 4 arranged thereinand locally welded thereto at the highest point 3. The freecrosssections of the conveyor pipe 2 and the bypass pipe 4 are in aratio of approximately 10 to l to one another. The conveyor pipeline 1comprises a connection 5 at which the conveyor pipe 2 is joined withflanges 6, 7, whilst the bypass pipe 4 comprises a socket joint 8, 9.The bypass pipe 4 is provided with openings 10a, 10b, 10c, 10d and 11a,11b, 11c, lid. The openings 10a, 10b, 10c, 10d act as outlet openingsbecause the carrier medium generally flows out of the bypass pipe 4through them into the conveyor pipe 2, whilst the openings 11a, 11b,11c, 11d are inlet openings because the carrier medium enters the bypasspipe 4 through them from the conveyor pipe 2.

The ends of the pipe wall downstream thereof project as pressed-intongues 12a, 12b, 12c and 12d into the free cross-section of the bypasspipe and block approximately 50 percent thereof, the upwardly projectingends of the tongues 12a to 12d being directed against the main conveyingdirection. The pressed-in tongues 13a, 13b, 13c and 13d of the inletopenings 11a to 11d are similarly formed, except that they only block 30percent of the free cross-section of the bypass pipe 4.

If a relatively long plug 14 of material is formed in the conveyor pipe2, the carrier medium flows exceptionally through the outlet opening aand the inlet opening 11a into and through the bypass pipe 4. The arrows15, 16, 17, 18 and 19 represent the streams of carrier medium at theindividual inlet and outlet openings 10a to 10d and 11a to 11d. Belowthe outlet opening 10b, some of the material has already been worn awayfrom the plug 14. The cross-section of the channel 20 thus formed iseven at this stage so great that the rate of flow of the carrier mediumin the channel 20 is no longer sufficient to entrain further material.As indicated by the arrows 16, the carrier medium now flows partlythrough the upper section of the bypass pipe 4 and partly from theoutlet opening 10b through the channel 20. The carrier medium thenreenters the bypass pipe 4 through the inlet opening 11b. Bydistributing the flow of carrier medium over a relatively largecrosssectional area in this way, the flow resistance generated by thetongues 12b and 13b in the bypass pipe is reduced.

By contrast, if the plug 14 of material is still blocking the opening100, the carrier medium is accelerated to .a relatively high rate offlow at the outlet opening 100 where it flows round the tongue 120 onaccount of the reduction in cross-section of the bypass pipe 4. Thedevice thus functions in the manner of an injector, the material 21being sucked through the inlet opening 11c into the bypass pipe 4 inwhich it is also greatly accelerated. As a result, pipe 4 is increased.The increase in the pressure loss has the same effect as partial closureof this section of the bypass pipe 4. The material carried through thebypass pipe 4, predominantly in the form of strands 23, is peeled off bythe tongue 12d of the outlet opening 10d and guided back into theconveyor pipe 2.

The static pressure prevailing upstream of the plug 14, which is onlyreduced by an amount corresponding to the relatively low flow resistanceof the outlet opening 10:: and inlet opening 11a, now acts through thebypass pipe 4 and the outlet opening 10c on the plug fragment situatedbetween the branch openings 10c and 10d in the direction of flow. Underthe effect of this pressure which on its own would not be sufficient toshift the entire plug 14 of material, the final plug fragment is brokenaway along the chain line 22.

The arrows 18 indicate the flow pattern at the outlet opening 10dnearest the end of the plug. After the fragment of plug between theoutlet openings 10c and 10d has been broken away, almost the entirecarrier medium flows out of the opening 100 into the conveyor pipe 2.The pressure loss of the bypass pipe 4 is reduced by an amountcorresponding to the flow resistance of that section of the bypass pipesituated above the separated plug 14. The reduction in the pressure lossis accompanied by an increase in the flow of carrier medium through thebypass pipe 4. As a result, the rate of flow of the carrier medium inthe bypass pipe 4 and in the channel 20 is increased. Once againmaterial is sucked through the inlet opening 11b into the bypass pipe 4and separation of the plug fragment furthest downstream takes place inthe same way as described with reference to the pipe section between theopenings 10c and 10d. This sequence of operations is then repeatedagainst the direction of flow.

What we claim is:

1. An apparatus for pneumatic or hydraulic conveying of bulk materialscomprising a conveyor pipeline and a by-pass pipe disposedlongitudinally within the conveyor pipe, the by-pass pipe having a freecrosssectional area of from 10 to 20 percent of the free cross-sectionalarea of the conveyor pipe, inlet openings and outlet openings at spacedintervals along the length of the pipe formed by radial cut-outs in theinwardly disposed side of the wall of the by-pass pipe communicating theby-pass pipe with the conveyor pipe, the end of the by-pass pipe wallimmediately downstream of each cut being bent inwardly and projecting asa tongue into the by-pass pipe against the main conveying direction andblocking from 10 to 90 percent of the free cross-section of the by-passpipe.

2. An apparatus as claimed in claim 1, wherein the inlet openings in theby-pass pipe are each located downstream of an outlet opening at adistance corresponding to between one and two times the internaldiameter of the by-pass pipe.

3. An apparatus as claimed in claim 2 wherein the tongues of the outletopenings block from 30 to 90 percent of the free cross-section of theby-pass pipe.

4. An apparatus as claimed in claim 3, wherein the tongues of the inletopenings block from l0 to percent of the free cross-section of theby-pass pipe.

5. An apparatus as claimed in claim 2 wherein the tongues of the inletopenings block from 10 to 70 percent of the free cross-section of theby-pass pipe.

6. An apparatus as claimed in claim 1 wherein the tongues of the outletopenings block from 30 to percent of the free cross-section of theby-pass pipe.

7. An apparatus as claimed in claim 1 wherein the tongues of the inletopenings block from 10 to 70 percent of the free cross-section of theby-pass pipe.

' l =1 t i

1. An apparatus for pneumatic or hydraulic conveying of bulk materialscomprising a conveyor pipeline and a by-pass pipe disposedlongitudinally within the conveyor pipe, the by-pass pipe having a freecross-sectional area of from 10 to 20 perCent of the freecross-sectional area of the conveyor pipe, inlet openings and outletopenings at spaced intervals along the length of the pipe formed byradial cut-outs in the inwardly disposed side of the wall of the by-passpipe communicating the by-pass pipe with the conveyor pipe, the end ofthe by-pass pipe wall immediately downstream of each cut being bentinwardly and projecting as a tongue into the by-pass pipe against themain conveying direction and blocking from 10 to 90 percent of the freecross-section of the by-pass pipe.
 2. An apparatus as claimed in claim1, wherein the inlet openings in the by-pass pipe are each locateddownstream of an outlet opening at a distance corresponding to betweenone and two times the internal diameter of the by-pass pipe.
 3. Anapparatus as claimed in claim 2 wherein the tongues of the outletopenings block from 30 to 90 percent of the free cross-section of theby-pass pipe.
 4. An apparatus as claimed in claim 3, wherein the tonguesof the inlet openings block from 10 to 70 percent of the freecross-section of the by-pass pipe.
 5. An apparatus as claimed in claim 2wherein the tongues of the inlet openings block from 10 to 70 percent ofthe free cross-section of the by-pass pipe.
 6. An apparatus as claimedin claim 1 wherein the tongues of the outlet openings block from 30 to90 percent of the free cross-section of the by-pass pipe.
 7. Anapparatus as claimed in claim 1 wherein the tongues of the inletopenings block from 10 to 70 percent of the free cross-section of theby-pass pipe.